An interferometric fiber optic gyroscope includes a light source that provides an optical signal to a fiber optic sensing coil. A typical light source includes a laser diode that provides pump light to a gain fiber. The gain fiber includes a dopant that absorbs pump light and then emits an optical signal that is suitable for delivery. Within the FOG, a multifunction integrated optic chip (MIOC) is connected to the fiber optic sensing coil. The MIOC includes components such as a polarizer, a phase modulator and a Y-coupler (splitter/combiner) that are used in processing and controlling optical signals input to and from the fiber optic sensing coil. The output of the FOG is an intensity that can be used to determine the phase difference between the two counter-propagating waves. A portion of the output is returned to the light source through a splitter and a second portion of the output is provided to a photodetector through the splitter for measuring the phase difference. The rotation rate of the coil about its sensing axis is obtained by dividing this phase difference by a scale factor of the FOG, referred to as the Sagnac scale factor.
The scale factor stability of fiber optic gyroscopes (FOGs) is affected by changes in the polarization state of the light in the fiber between the optical source and the MIOC. Polarization dependent loss in optical components, a type of unwanted optical filtering, results in asymmetric optical polarization. Degradation of polarization state symmetry changes the scale factor of the FOG via optical filtering of the light when the traversing first the section between the source and the MIOC then traversing the polarizing MIOC itself. This optical filtering can lead to short term scale factor instability and long term degradation of the scale factor repeatability.
Another area where gyroscopic errors can occur is in the optical source used to drive the MIOC. For instance, some optical sources use a wavelength division multiplexor (WDM) in an attempt to provide a stabilized light source to drive the MIOC. The WDM is constructed as a fused taper coupler where such construction is prone to large polarization dependent loss resulting in wavelength asymmetry when evaluated through an optical polarizer. Such construction is also prone to wavelength instability as a function of time and temperature resulting in a net gyro scale factor error when used to drive the FOG. The cross coupling point along the optical path results in a temperature varying sinusoidal gyro scale factor error.